Paramecia detect soluble chemicals in their environment and respond to them by accumulating or dispersing. They accomplish this population behavior by altering frequency of random turns or swimming speed, that is, by chemokinesis (often called chemotaxis). The described project approaches Paramecium chemokinesis as a chemosensory transduction pathway in which external chemical cues are detected by the cell; the chemical cues are transduced into membrane electrical cues; electrical properties control ciliary beating patterns, hence, the cells alter their swimming in response; and these alterations cause populations of cells to accumulate or disperse. Paramecia can be considered models of excitable cells and chemoreception systems involved in neurotransmission, gustation or olfaction. However, paramecia, unlike most other chemoreception systems, are amenable to many varied approaches including 1) intracellular recordings of membrane electrical correlates of chemokinesis; 2) crosses and complementation tests of organization of genes that control chemoresponse behavior; 3) membrane biochemistry for isolation and identification of membrane proteins; 4) video analysis of ciliary beating and motile mechanisms that lead to accumulation or dispersal of a population. Previously, we have generated mutants to probe at random steps in the chemosensory pathway from receptor to effector (the cilia). We propose now to genetically analyze mutants with defects in chemoreception and use subsets of these mutants in comparison with normal cells in the following studies: 1) Using electrophysiology, we will analyze the mechanisms of transduction of 3 structurally different attractant chemical cues into membrane electrical cues. These 3 attractants cause similar membrane potential changes, but perhaps by different ionic mechanisms. 2) S-adenosyl-methionine (SAM) has the unusual effect of changing paramecia's normal attraction response to acetate into repulsion. We will characterize the behavioral and membrane electrical effects of SAM on cells and test the possibility of methyl transfer in the SAM effect. Paramecia adapt and stop responding to chemicals, as other chemoreception systems do. We will use information gathered in 1) above to begin a description of adaptation. Reversion analysis will be included in the genetic study to identify chemoreception gene product interactions.